Finely divided crystalline limestone in heavy fluid for float-and-sink concentration



April 20, 1

948- J. A. BRussET 2,440,005

FINELY DIVIDED CRYSTALLINE LIMESTONE IN HEAVY FLUID FOR FI.1OATANDSI11Kl CONCENTRATION Filed March 19, 1945 Per Cen. Recovery by /Ve/'qb P en Recovery by Weib/ff Por Genf: sl: by Mfg/ff Per Gent @ecm/ery by h/e/'gb Patented Apr. 20, 1948 FINELY DIVIDED IN HEAVY FLUID CONCENTRATION Jean Albert Brusset,

assignor to McNally This invention relates to the coal by a gravity concentration of the oat-andsink type, and is particularly concerned with the provision of an improved suspending medium or heavy iluid for use in the said process of separating coal from slate and other refuse.

In such processes, the suspending solid is so selected, and the proportion of solid to suspending liquid (usually water) usually is so adjusted that the resulting heavy uid has a specific gravity varying, according to requirements of each special coal, between 1.30 and about 1.70. There are a great many solids having specic gravities which would be operable were specific gravity the only criterion; however, there exist a number of other criteria which, in effect. greatly narrow the ileld of operable solids.

Contrary to the prior v"art proposals, the new flotation medium of the present invention consists essentially of an aqueous suspension of tinely divided, hard crystalline limestock rock (specifically metamorphosed vlimestones of the consistency oi marble) of high purity, particularly as regards freedom from quartz, shales and clay, said aqueous suspension being in suilicient concentration to provide a medium of required speclc gravity. The limestone. which should have a hardness of 3 or only very slightly less than 3, should be as viree as possible from shales and clay, in order to minimize the introduction of ultrane particles into the medium: it should be as free as possible from quartz, in order to depress abrasion oi the equipment in which the medium is handled. I have found that properly subdivided, hard crystalline limestone rock ofthe purityk described. deposits of which occur in the Province of British Columbia, Canada, and elsewhere throughout the Dominion of Canada and the United States of suspensions in water, and all specific gravities of otation medium, between 1.30 and 1.70, can readily be provided without undue viscosity of the medium at the higher values. The limestone particles desirably resist disintegration during use and handling of the medium containing them and their aqueous suspension does not-tend to become colloidal in character.

I have discovered that for optimum separation art of cleaning I caYsTALuNE LIMEs'roNE FOR.I FLOAT-AND-SINK Blairmore, Alberta, Canada,

Pittsburg Manufacturing Corporation, Pittsburg, Kans.

Application March 19, 1945, Serial No. 583,608 In Canada July 20, 1944 4 Claims. (Cl. 209-173) of coal from shale, slate and other heavy refuse the hard crystalline limestone rock should be so ground or otherwise subdivided Ithat substantially all of the material is minus 48 mesh, that from about 30 to about 35% thereof is minus 48 plus 100 mesh, that from about 40 to about 50% thereof is minus 100 mesh, and that from about 20 to about 25% is minus 200 mesh. The subdivided limestone rock may contain a few percent. of plus 48 mesh particles, say, 5% of minus 40 plus 48 mesh material, without destroying its operability.

The suspension medium of the present invention, consisting of an aqueous suspension of the r 1.70, with the above preferred America, makes very stable aforesaid subdivided limestone. possesses a number of advantages over previously proposed media; thus, the solid ingredient, viz., the hard crystalline limestone of desirable purity. is readily and widely available; it is easily reduced to the required mesh, and, -in the course of being subdivided, does not tend to yield a large amount of ultrafine particles; in use it does not quickly disintegrate to colloidal particles; it ls not abrasive on the machinery; it remains readily in suspension; being desirably free from ultrafine particles, it does not stick to the finished products but rather is easily washed oil of them; and it is easily recovered from the wash water by cycloning so that recycling is facilitated.

The special advantages accruing from using a subdivided hard, crystalline limestone rock having the above stated preferred size distribution are: (1) the rate of settling of the resulting water-limestone medium for the specic gravity range 1.30-1.70 is sufciently low that the medium can easily be kept in suspension; and (2) the viscosity of the medium, at speciilc gravity 1.30-

size composition clean and at the between coal and is low enough to give a very same time rapid separation as refuse.

The preparation of a heavy il-uid suspending medium, having a specific gravity anywhere between about 1.30 and about 1.70, from water (or y other operable suspending liquid) and the above described suspending solid can be eil'ected by well known technique, to the end that said heavy fluid iioats the coal but not the slate or other refuse.V

The resulting heavy iluid may be used either in 2 inches and then t0 1A coal. a heaviest portion subst of heavy refuse. and an inte dling" portion which may be i' discarded. or used as such. Af the separated portions of com ter may be washed to remove therefrom adherand the suspending mereuse ina cyclical repetition of the process. Such cyclical process, and

ing suspending medium. dium may be reformed for apparatus for use therein,

in my U. S. Patent N0. 2,356,648.

The invention will nowdetall with reference to illustrative example:

The raw material for preparin was a hard,compact, of high purity and substantially free from quartz, shales and clay, taken from a deposit at Crowsnest, Province of The rock had a hardness of 3. The rock analyzed: free Sim-0.9%; oxides of Fe and Al-0.25% This raw material was nely in the present process, in the following manner: the rock was crushed ilrst to inch; the 1A inch material in a Bradley until 20% thereof passed a 200 The resulting subdivided limeston lowing particle size distribution:

solid of the heavy fluid crystalline limestone rock,

British Columbia, Canada.

lugo-1.25%. divided, for use thereupon was ground three com the raw coal into two refuse); or. it may .be involved separation of ponents. viz., a substantially pure antially consisting mediate or "midurther dressed, or ter the removal of ponents, these lat- -mesh screen. e had the folloid-like) particles. A "heavy uid stone by agitatingl 56% 44% of water, yielding speciilc gravity of 1.55.

Alberta, Canada, and

3 products, as follows:

It was substantially free from ulti-anne (or, c01- suspending medium for cleaning coal was prepared from this subdivided limeby weight thereof with a suspension having a l/2 inch via'e broadly described l5 Percent e Ash Content by Weig t Per cent be described in further C] C l the following specific Mun::::::::::::::::::::::: fig Refuse 27l 54.00 g the suspending characteristics.

At 1.55 specific on the plus-and-minus 0.10%

distribution curve (see Bureau of roller mill G. D. Coe), which The above specic example data are typical of the results being obtained in the large scale, commercial working of the above-described process, at the washery of the above-named mine, in the cleaning of a coal of acknowledgedly bad washing gravitg it has an index of 17 speciic gravity Mines Information Circular 7045, December 1938, entitled An Explanation of Washability Curves for the Interpretation of Float-and-Sink Data on Coal," by means an extremely diillcult separation between coal and refuse-as is acknowledged by all experts in coal-washing. The

three figures of the appended drawing constitute Per cent a set of curves of washability, including the Minus 48 mesh-plus 100 mesh about 30.0 1-0.10% curve, as determined by laboratory tests Minus 100 mesh-plus 200 mesh about 50.0 on the 0.5"5.0" portion of this coal, said curves Minus 200 mesh 20.0 having been derived from the data set out in the three gravimetric analyses and ash distribution 100.0 Tables I, II and III immediately following: I. Re Fig. 1; size range, minus 5 in., plus 1% in.

Cumulative Specific Gravity Actual Products Plsiiffsd' sinkings rloatmgs 0 10 sp. gy

Per cent Per cent Per cent Per cent Per cent Per cent Sink F10 Wc. Ash Wt. A511 'W6 Aan II. Re Fig. 2 size range, minus 1% in., plus in.

Cumulative Spcciilc Gravity P1 d Actual Products 11S-811 m us Smkings Floatings 0.10 sp. gy.

Per cent Per cent Per cent Per cent Per cent Per cent Smk F 10st Wt. Ash wt. Ash Wt. Ash

.... 1.3 16.3 4.6 63.7 26.0 16.3 4.6 1. 3 1. 4 56.1 31. 7 6. 6 52. 0 40.1 46. 0 7. 2 1.4 1.5 gj'l 16.0 16.6 36.0 50.4 64.0 9.6 1. 5 1. 6 jg 9. 6 26. s 26. 4 56. 2 73. 6 12.1 1. 6 1(7)' g 3. 6 37. 6 22. 6 61. 6 77. 2 13. 3 1.7 22.6 61.6 100.0 24.3

III. Re Fig. 3; -size range, minus 3/4 in.. plus 1/2 in.

Cumulative Specific Gravity Actual Products Pllxllsihaad' Slnkings Floatings 0.10 sp. gy.

Per cent Per cent Per cent Por cent Per cent Per cent Sink om wt. Ash wt. ash wt. Ash

1.3 20.0 4.7 80.0 29.0 20.0V 4.7 1.a 1.4 g1g 27. 4 0.0 52. e 40.8 47. 4 7.2 1. 4 1. 5 251g 1s. 4 1s. s 34. 2 53. o es. s 10. 3 1.0 1.0 7.0 30.0 20.3 59.0 73.7 12.5 1.0 1.7 12 3.6 37.3 :r2.7 y03.0 77.3 13.6 1.7 22.7 03.0 100.0 n.9

In each of Figs. 1, 2 and 3, curve I is the specic gravity curve, curve II is the plusand-minus 0.10% specic gravity distribution curve, curve 11.1" is the cumulative float ash curve, and curve IV" is the cumulative sink ash curve.

The industrial plant obtains a better refuse than seems possible under the laboratory tests, because the middllngs are separated from the refuse in the large scale plant.

I claim:

1. The method of separating particles of coal from a mixture thereof with particles of heavy refuse, which comprises forming an aqueous suspension of finely divided crystalline limestone substantially free from quartz and from components which tend readily to disintegrate through use and handling into ultra-fine particles, said limestone having a hardness of about 3, practically all o! which finely divided limestone is of a degree of fineness to pass a 48 mesh screen, a large fraction thereof being minus 100 mesh and a minor but substantial part thereof, not exceeding about 25% by weight, being minus 200 mesh in particle size, introducing the mixture into a bath of said aqueous suspension of finely divided limestone, adjusting and maintaining the density of the aqueous suspension at such a. value that the coal particles oat on said bath but the particles of heavy refuse sink therein, and separately removing coal particles and particles of heavy refuse from said bath.

2. A suspending medium for separating coal from a mixture thereof with particles of heavy refuse by the float-and-sink method, said sinkand-iioat medium being an aqueous suspension, having a specific gravity between 1.30 and about 1.70, of finely divided, hard, crystalline limestone rock having a hardness of about 3. said limestone rock being substantially free from quartz and from components which tend readily to disintegrate through use and handling into ultraiine particles, practically all of which finely divided limestone is o! a degree of iineness to pass a 48 mesh screen, a large fraction thereof being minus 100 mesh and a minor but substantial part thereof, not exceeding about 25% by weight, being minus 200 mesh in particle size.

3. A suspending medium for separating coal from a mixture thereof with particles of heavy refuse by the iloat-and-sink method, said sinkand-float medium being an aqueous suspension, having a specific gravity between about 1.30 and about 1.70, of finely divided, hard, crystalline limestone rock having ahardness of about 3, said limestone rock being substantially free from quartz and from components which tend readily to disintegrate through use and handling into finely divided ultra-ne particles. at least about 95% of which limestone is minus 48 mesh, from about 60 to about 75% is minus 100 mesh, and at least about 20% but not more than about 25% is minus 200 mesh in particle size'.

4. A suspending medium for separating coal from a mixture thereof with particles of heavy refuse by the float-andsink method, said sinkand-float medium being an aqueous suspension. having a specific gravity between about 1.30 and about 1.70, of nely divided, hard,.crystalline limestone rock substantially free from quartz and from components which tend readily to disintegrate through use and handling into ultra-ilne particles, said :dnely divided limestone having a hardness of about 3 and the approximate size distribution'.

. Per cent Through 48 mesh, on 100 mesh 30.0

Through 100 mesh, on 200 mesh 50.0

50 Through 200 20.0

mesh

. JEAN ALBERT BRUSSET.

REFERENCES CITED The following references are of record in the 111e of this patent:

UNITED STATES PATENTS Number 

